Patent application title: PRESSURE SENSOR

Abstract:

The invention relates to a pressure sensor (6). This pressure sensor (6)
comprises a flexible membrane (11) cooperating with a transmission device
(10) that enables a value representing the pressure to be supplied on the
basis of the deformation of the membrane (11). The membrane (11) is made
from an at least partially amorphous material in order to optimise the
dimensions of the sensor (6).

Claims:

1-10. (canceled)

11. A pressure sensor comprising a flexible membrane cooperating with a
transmission device that enables a value representing the pressure to be
supplied on the basis of the deformation of said membrane, wherein the
membrane is made from an at least partially amorphous metal alloy in
order to optimise the dimensions of said sensor, wherein the metal alloy
comprises at least one precious type element included in the list
comprising gold, platinum, palladium, rhenium, ruthenium, rhodium,
silver, iridium or osmium.

12. The pressure sensor according to claim 11, wherein the membrane is
made of a completely amorphous material.

13. The pressure sensor according to claim 11, wherein the material has a
ratio of elastic limit to its Young's modulus of more than 0.01.

14. The pressure sensor according to claim 13, wherein the material has a
Young's modulus of more than 50 GPa.

15. The pressure sensor according to claim 11, wherein the membrane is
substantially discoidal and is secured to said sensor by its periphery.

16. The pressure sensor according to claim 11, wherein the membrane has a
non-rectilinear profile in order to increase its deformation surface.

17. The pressure sensor according to claim 16, wherein the profile of the
membrane has at least one sinusoidal portion.

18. A watch, wherein it comprises a pressure sensor according to claim 11.

19. The watch according to claim 18, wherein it additionally comprises a
means for converting said value representing the pressure into a depth
value to allow said watch to perform a depth gauge function.

20. The pressure sensor according to claim 12, wherein the material has a
ratio of elastic limit to its Young's modulus of more than 0.01.

21. A watch, wherein it comprises a pressure sensor according to claim 12.

22. A watch, wherein it comprises a pressure sensor according to claim 13.

23. A watch, wherein it comprises a pressure sensor according to claim 14.

24. A watch, wherein it comprises a pressure sensor according to claim 15.

25. A watch, wherein it comprises a pressure sensor according to claim 16.

26. A watch, wherein it comprises a pressure sensor according to claim 17.

Description:

[0001]The present invention relates to a pressure sensor using a flexible
membrane. This membrane cooperates with a transmission device that
enables a value representing the pressure to be supplied on the basis of
the deformation of said membrane.

TECHNOLOGICAL BACKGROUND

[0002]A dive watch is known in the prior art that comprises a case, which
bears a pressure sensor comprising a membrane and a transmission device.
The membrane is capable of deforming mechanically under the effect of
external pressure to then act on the transmission device. This device
thus transmits said deformation movement representing the pressure in
order to be amplified, for example, so that the pressure value detected
by the sensor is displayed.

[0003]In general, the membrane of this sensor is made from crystalline
material such as e.g. an alloy composed of copper and beryllium (Cu--Be).

[0004]Every material is characterised by its Young's modulus E, also
called elasticity modulus (generally expressed in GPa), which
characterises its resistance to deformation. Moreover, every material is
also characterised by its elastic limit σe (generally
expressed in GPa), which represents the stress beyond which the material
will plastically deform. Thus, it is possible, for a given thickness, to
compare materials by establishing for each one the ratio of their elastic
limit to their Young's modulus σe/E, wherein said ratio is
representative of the elastic deformation of each material. Therefore,
the higher this ratio is, the greater the elastic deformation of the
material. Crystalline materials such as those used in the prior art, e.g.
the alloy Cu--Be, which has a Young's modulus E equal to 130 GPa and an
elastic limit σe that typically amounts to 1 GPa, give a low
σe/E ratio, i.e. in the order of 0.007. These crystalline
alloy membranes therefore have a limited elastic deformation. In the case
of the membrane of a pressure sensor, this means a limited measurement
range.

[0005]Moreover, because this elastic limit is low, when it deforms the
membrane approaches its region of plastic deformation under low stresses
with the risk that it cannot resume its initial form. To avoid such a
deformation, the deformation of the membrane is restricted, i.e. the
amplitude of the movement of the membrane is intentionally limited. It is
then understood that the transmission movement must be amplified. This
results in noise that is detrimental to the pressure sensor and,
moreover, to the display of the pressure value.

[0006]In addition, the use of precious crystalline metals for the
production of such a pressure sensor membrane, or any other active
element of a timepiece, is not conceivable considering the inadequate
mechanical characteristics of these metals. In fact, these precious
metals in particular have a low elastic limit in the order of 0.5 GPa in
the case of alloys of Au, Pt, Pd and Ag, as opposed to about 1GPA in the
case of the crystalline alloys classically used in the production of
pressure membranes. In view of the elasticity modulus of these precious
metals, which is in the order of 120 GPa, a σe/E ratio of
about 0.004 is obtained. However, a high σe/E ratio is
necessary for the production of such a membrane, as explained above.

[0007]Consequently, the person skilled in the art is not encouraged to use
these precious metals for the production of such a membrane.

SUMMARY OF THE INVENTION

[0008]The invention relates to a pressure sensor that remedies the
abovementioned disadvantages of the prior art by proposing a more
reliable membrane that has a safety margin in relation to the maximum
stress applied, while also allowing a more significant deformation
amplitude. Alternatively, the invention proposes a membrane that allows
an equivalent deformation amplitude for smaller dimensions.

[0009]On this basis, the invention relates to the pressure sensor
described above, in which the membrane is made from an at least partially
amorphous metal alloy in order to optimise the dimensions of said sensor
and characterised in that the metal alloy comprises at least one precious
type element or one of these alloys included in the list comprising gold,
platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or
osmium.

[0010]Advantageous embodiments of this sensor are disclosed in dependent
claims 2 to 8.

[0011]Surprisingly, precious metals in amorphous form have a high
σe/E ratio that allows the production of parts such as the
membrane according to the invention.

[0012]A first advantage of the membrane according to the present invention
is that it has elastic characteristics that are of greater interest. In
fact, in the case of an amorphous material, the σe/E ratio is
increased by increase of the elastic limit σe. Thus, the
stress, above which the material does not resume its initial form, is
increased. This improvement in the σe/E ratio thus allows a
more significant deformation. This enables the dimensions of the membrane
to be optimised, depending on whether the range of measurement of the
membrane is to be increased or the size of said membrane is to be reduced
for an equivalent range of measurement.

[0013]Another advantage of these amorphous materials is that they open up
new possibilities for shaping to allow the design of parts with
complicated shapes with a much higher precision. In fact, amorphous
metals have the particular characteristic of softening while remaining
amorphous in a given temperature range [Tx-Tg] inherent to each alloy
(where Tx: crystallisation temperature and Tg: glass transition
temperature). It is therefore possible to shape them under a relatively
low stress at a moderate temperature. This then allows fine geometries to
be reproduced very precisely, since the viscosity of the alloy decreases
severely and this alloy thus moulds to all the details of the mould.

[0014]In addition, the invention also relates to a watch characterised in
that it comprises a pressure sensor having a membrane that is consistent
with the above explanation. An advantageous embodiment of this watch is
the subject of dependent claim 10.

BRIEF DESCRIPTION OF THE FIGURES

[0015]The purposes, advantages and features of the watch according to the
present invention will be made clearer in the following detailed
description of at least one embodiment of the invention given solely by
way of non-restrictive example and illustrated by the attached drawings:

[0016]FIG. 1 is a schematic sectional view of a watch comprising a
membrane according to the present invention;

[0017]FIG. 2 is a schematic sectional view of a watch comprising the
membrane according to the present invention when this is subjected to
external pressure;

[0018]FIG. 3 is a schematic representation of a preferred embodiment of
the membrane according to the present invention;

[0019]FIG. 4 shows a watch comprising the membrane according to said
preferred embodiment; and

[0020]FIG. 5 shows deformation curves for a crystalline material and for
an amorphous material.

DETAILED DESCRIPTION

[0021]FIGS. 1 and 2 are sectional views of a dive watch 1 composed of a
sub-structure 2, on which a bezel 3 bearing a glass 4 of the watch 1 is
secured. A display unit 5 also secured to the sub-structure 2 is arranged
under the glass 4.

[0022]The watch 1 is closed by a base 7 that is tightly secured to an
intermediate section 8 that is itself tightly secured to the
sub-structure 2, thus forming a case. The watch also comprises a pressure
sensor 6 that is preferably located inside this case 21.

[0023]The pressure sensor 6 comprises a transmission device 10 as well as
a membrane 11 that is mounted to form a sealed cavity 9. The membrane 11
is located inside the case 21 of the watch 1 and secured onto a support
12 at its periphery. This allows a favourable deformation of the membrane
11 to be assured. In our example, the support 12 is secured to the
intermediate part 8. To ensure that the membrane 11 is in contact with
the outside environment, the base 7 of the case 21 is pierced by several
orifices 13. These orifices 13 allow the membrane to deform if the
pressure is different on either side of the membrane 11, as shown in FIG.
2.

[0024]Moreover, it can be provided that the base 7 of the case 21 is
fitted with a removable cover 14 that can be secured by clipping in place
in order to block the orifices 13 when a pressure measurement is not
required. This provides protection for the pressure sensor 6.

[0025]For operation of the pressure sensor 6, the transmission device 10
is used in conjunction with said membrane 11. Thus, under the effect of
the pressure difference between the sealed cavity 9 and the outside
environment, the membrane 11 will deform to a greater or lesser extent.
In fact, if the external pressure is greater than the pressure inside the
sealed cavity 9, then the membrane 11 will deform in order to constrict
the volume of the sealed cavity 9, as may be seen in FIG. 2.

[0026]This deformation of the membrane 11 will act on the transmission
device 10, which will detect the position of the membrane 11 in relation
to its initial position. The initial position is preferably that in which
the pressures on either side of the membrane 11 are equal. Once the
detection has occurred, the transmission device 10 will transmit this
deformation of the membrane 11 by a mechanical movement, for example.

[0027]This movement representing the pressure transmitted by the device 10
can then possibly be amplified, then used by the display device 5. This
latter device will use a means for converting this movement representing
the deformation, and therefore the pressure, into a depth value. This
device 5 will then display the depth measured by the pressure sensor 6.
It can, of course, be provided that the pressure is detected by any other
means such as a piezoelectric transducer. Moreover, other functions that
make use of this pressure such as an altimeter or weather forecasting
function are possible.

[0028]The elements of the sensor 6 are therefore calibrated using
predetermined load specifications defining the desired range of
measurement for the displacement of the membrane 11. The desired range of
measurement represents the maximum pressure value that one wishes to
detect and display, e.g. a depth of 100 metres. The displacement of the
membrane 11 defines the maximum deformation that said membrane 11 can
make. Thus, the characteristics of the membrane 11 are then defined on
the basis of these two values. Said membrane is characterised by its
dimensions (diameter and thickness in the case of a circular membrane 11
of the present example) and by the material it is made of.

[0029]Advantageously, according to the invention the membrane 11 consists
of an amorphous or partially amorphous material. In particular, metallic
glasses, i.e. amorphous metal alloys, are used to form the membrane 11.

[0030]In fact, the advantage in terms of deformation of these amorphous
metal alloys comes from the fact that during their production, the atoms
forming this amorphous material are not arranged in any particular
structure, as is the case with crystalline materials. Therefore, even if
the Young's modulus of a crystalline material and an amorphous material
is identical, the elastic limit, σe, is different. In fact,
the amorphous material is distinguished by a higher elastic limit or
σea than that of the crystalline material with a ratio
essentially equal to two, as shown in FIG. 5. This figure shows the curve
of the stress σ as a function of the deformation a for an amorphous
material (in dotted lines) and for a crystalline material. This means
that amorphous materials can be subjected to a higher stress before
reaching the elastic limit σe.

[0031]Firstly, this membrane 11 made of amorphous material thus allows the
reliability of the pressure sensor 6 to be improved compared to a
membrane 11 made of crystalline material. In fact, the elastic limit
σea is higher and this means the plastic region is further
away, thus reducing the risk of plastic deformation of the membrane.

[0032]Moreover, this ability to elastically withstand a higher stress
allows a larger range of measurement to be conceivable.

[0033]Moreover, advantageously, it is found that in the case of a membrane
11 made of amorphous material its dimensions can also be optimised when
the same stress is applied centrally in order to cover an equivalent
displacement. In fact, the dimensions of the membrane 11 modify its
deformation. Thus, if the diameter increases, then the theoretical
displacement of the membrane increases. Moreover, if the thickness
increases, the theoretical displacement of the membrane 11 decreases.
Advantageously, in the case of an elastic limit that increases, the
stress that can be applied to the membrane 11 without plastic deformation
also increases. It thus becomes possible to retain the same movement
amplitude by reducing its diameter and its thickness.

[0034]With respect to the material itself, it can firstly be noted that
the higher the σe/E ratio, the more effective the sensor.
Advantageously, the materials in which the σe/E ratio is
higher than 0.01 are the most appropriate materials for the formation of
a pressure sensor membrane 11. It can also be specified that apart from
the σe/E ratio, the value of E can also be selected to be
higher than a certain limit so that the pressure sensor can be contained
in an acceptable space. This limit is preferably set at 50 GPa.

[0035]A certain number of characteristics can then be taken into account.
Thus, it can be considered that the characteristics of corrosion
resistance and non-magnetic characteristics are particularly relevant for
a dive watch.

[0036]Hence, examples of amorphous materials that can be used can be
cited. Therefore, by way of example, Zr41Ti14Cu12Ni10Be23, for which the
Young's modulus E amounts to 105 GPa and the elastic limit amounts to
σe=1.9 GPa, has a σe/E ratio=0.018, and
Pt57.5Cu14.7Ni5.3P22.3, for which the Young's modulus E amounts to 98 GPa
and the elastic limit amounts to σe=1.4 GPa, has a
σe/E ratio=0.014.

[0037]Naturally, there are other characteristics that can be of interest,
such as the allergenic status of the alloy. In fact, it may be noted that
the materials, whether crystalline or amorphous, often use alloys
comprising allergenic elements. For example, such types of alloys
comprise cobalt, beryllium or nickel. Therefore, variants of the membrane
11 according to the invention can be formed using alloys that do not
contain these allergenic elements. It can also be provided that
allergenic elements are present, but these do not cause any allergenic
reaction. For this, it can be provided that the membrane 11 that contains
these allergenic elements does not release them when corrosion attacks
the membrane 11.

[0038]According to another variant of the invention, it can be provided
that the membrane 11 is made of noble material. In fact, in crystalline
state, noble materials such as gold or platinum are too soft to allow the
formation of a flexible and strong membrane 11. However, when they are
present in metallic glass form, i.e. in amorphous state, these precious
metals then have characteristics that enable them to be used to produce a
membrane 11 for a pressure sensor, while also allowing a luxurious and
aesthetically pleasing appearance. Platinum 850 (Pt 850) and gold 750 (Au
750) are the preferred precious metals to be used for the production of
said membrane 11. Naturally, other precious metals could also be used
such as palladium, rhenium, ruthenium, rhodium, silver, iridium and
osmium.

[0039]It can also be noted that amorphous metal alloys are readily shaped.
In fact, amorphous metals have the particular characteristic of softening
while remaining amorphous in a given temperature range (Tx-Tg) inherent
to each alloy. It is therefore possible to shape them under a relatively
low stress and at a temperature that is not too high.

[0040]This process consists of hot forming an amorphous preform. This
preform is obtained by melting metal elements forming the amorphous alloy
in an oven. This melting is controlled so that any contamination of the
alloy with oxygen is as low as possible. Once these elements are melted,
they are cast in semi-finished form, e.g. as a disc with dimensions close
to the membrane 11, then cooled rapidly to retain the amorphous state.
Once the preform is made, hot forming is conducted in order to obtain the
finished part. This hot forming is conducted by pressing in a temperature
range between Tg and Tx for a determined time to retain a totally or
partially amorphous structure. This is done in order to retain the
characteristic elastic properties of the amorphous metals. The different
steps of the final shaping of the membrane 11 are therefore: [0041]a)
heating matrixes that have the negative form of the membrane 11 to a
selected temperature, [0042]b) inserting an amorphous metal disc between
the hot matrixes, [0043]c) applying a closing force to the matrixes in
order to replicate the geometry of these on the amorphous metal disc,
[0044]d) waiting for a selected maximum period, [0045]e) opening the
matrixes, [0046]f) rapidly cooling the membrane 11 below Tg, and [0047]g)
removing the membrane 11 from the matrixes.

[0048]This method of forming enables fine geometries to be reproduced with
high precision, since the viscosity of the alloy decreases severely, and
this can then mould to all the details of the mould. The advantage of
this method is that there is no hardening shrinkage, and this permits a
more precise part to be formed at a lower temperature than by injection
moulding.

[0049]Naturally, other types of shaping process are possible such as
injection moulding. This process consists of moulding the alloy obtained
by melting metal elements in an oven into any shape whatever, such as a
bar, in either a crystalline or an amorphous state. This alloy part of
whatever shape is melted again to be injected into a mould that has the
shape of the final part. Once the mould is full, it is cooled rapidly to
a temperature below Tg in order to avoid crystallisation of the alloy and
thus obtain a membrane 11 made of amorphous or semi-amorphous metal.

[0050]Thus, it is possible to shape the membrane 11 according to the
desired geometry. For example, it is possible to shape the profile of the
membrane 11 in order to modify its properties in the same way as its
thickness and its diameter. By way of example, it is possible to mould
the membrane 11 in order to obtain a sinusoidal profile, as shown in
FIGS. 3 and 4. Such a shape enables the surface of the membrane 11 to be
increased as well as its rigidity. The membrane 11 is therefore harder to
deform. This configuration of the section advantageously also allows the
elastic deformation of the material to be linearised as a function of the
pressure. This linearisation thus assists in simplifying the means of
converting the deformation of the membrane 11 to a pressure value.

[0051]It must be understood that various modifications and/or improvements
and/or combinations obvious to the skilled person can be applied to the
different embodiments of the invention discussed above without departing
from the invention as defined by the attached claims. For example, the
membrane has a different shape.